Antenna element including means for providing zero-error 180{20 {11 phase shift

ABSTRACT

A system including an antenna, such as a phased array radiating element including a dipole, is provided including a digital phase shifter. The 180* bit of the digital phase shifter is implemented by reversing the polarity of the signal in the antenna.

United States Patent [191 nu 3,803,621 Britt [45] Apr. 9, 1974 [54] ANTENNA ELEMENT INCLUDING MEANS 2,422,076 6; 1947 CBrown 3321/354 2,350,747 6 1944 arnet 3 54 ISSRSIIIIING ZERO ERROR 180 3,l76,297 3/1965 Forsberg 343/854 2,188,649 H1940 Carter 343/854 [75] inventor: Pope Patterson Britt, Utica, N.Y. 3295.134 12/ 1966 Lowe 343/854 [73] Assignee: General Electric Company, Utica,

N'Y' Primary Examiner- Eli Lieberman [22] Filed: Dec. 20, 1971 [2l] Appl. No.: 209,538

[57] ABSTRACT [52] U.S. Cl. 343/821, 343/854, 333/84 M [51] Int. Cl. H0lq 3/26 A system including an antenna, such as a phased array [58] Field of Search 343/854, 821; 333/31 R, radiating element including a dipole, is provided in- 333/84 M cluding a digital phase shifter. The 180 bit of the digital phase shifter is implemented by reversing the po- [56] References Cited larty of the signal in the antenna.

UNITED STATES PATENTS I 3,568,097 3/1971 Hyltn 333/31 2 Claims, 5 Drawing Figures PATEMEDAPR slam 3.801621 POPE P. BRITT,

HIS ATTORNEY.

1 AN'rENNA ELEMENT INCLUDING MEANS FOR This invention relates to microwave antennas. More specifically, it relates to phase shifting systems incorporated in microwave antennas.

An antenna element may be used for radiating or receiving. An example of a radiating element is a phase shifting radiator. One application for phase shifting radiators is found in the phased array. A phased array is a system in which many small antennas which remain physically fixed in position replace one large antenna which is moved in order to steer a transmitted beam. The phased array may, for example, comprise 2,000 radiating elements transmitting a power of 4 watts each rather than one large antenna radiating 8,000 watts. Steering of the beam transmitted by the phased array is accomplished by varying the relative phase of the radio frequency at the various array elements. Therefore, each phased array element must include means for phase shifting the radiation supply from a source to an antenna. (For purposes of this description, the term phased array element includes a system including an antenna and a radio frequency feed for connection to a source of transmitting transmission energy.) One prevalent form of phase shifter incorporated in they phased array element is the digital phase shifter.

The digital phase shifter includes discrete portions which are selectively used in various permentations to provide from zero to substantially 360 phase shift. Each discrete portion is called a bit. Commonly, a digital phase shifter includes 180, 90, 45 and 221 bits connected in series. A prevalent form of implementation of bits is called the loaded line arrangement. Commonly, two diodes are included in the 22%" and 45 bits while four diodes are included in the 90 and 180 bits. Due to bandwidth limitations in the design of conventional bits and non-uniformities in diode construction, errors in the phase shift produced by each bit may be equal to significant percentages of the phase shift it is supposed to provide. Where phase Shifters are constructed in microelectronic form, it may be impossible to select matched groups of diodes for construction of a bit. Among the reasons for this are that the diodes may be on the order of thousands of an inch wide and not susceptible to the same handling that discrete diodes are. Also, in the course of efficient manufacture of bits, the entire bit may be deposited on a substrate at once, and there is no opportunity to select and assemble diodes discretely. Since the 180 bit produces the largest phase shift, the largest errors, as measured in degrees, are associated with the 180 bit (although it may produce no greater percentage error than other bits).

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a digital phase shifter including a zero error 180 bit.

lt is a more specific object of the present invention to provide 180 phase shift in an antenna element, which phase shift is constant irrespective of frequency.

lt is also an object of the present invention to provide a phase shifting antenna element in which errors in providing phase shift due to design limitations and nOn-uniformities Of components are eliminated.

It is a further object to provide an antenna element of the type described in which adverse affects produced by non-uniformities in components is minimized.

It is another object of the present invention to provide an antenna element of the typedescribed in which a change of state of the 180 bit does not change the impedance of the antenna element.

Briefly stated, in accordance with the present invention, there is provided, in an antenna element a system in which transmission and phase shifting functions are integrated in a single structure. Phase shift in increments of less than 180 is provided in a conventional manner. Phase shifting means utilized are connected in series with a 180 bit comprising-means for reversing the polarity of radiation applied thereto. The antenna element may be utilized for radiating or receiving.

BRIEF DESCRIPTION OF THE DRAWINGS The means through which the foregoing objects and features of novelty are accomplishedare pointed out with particularity in the claims forming the concluding portion of the specification. The invention, both as to its organization and manner of operation may be further understood by reference to the foregoing description taken in connection with the following drawings.

Of the drawings:

FIG. l is an illustration,` partially in schematic form of a plan view of a microstrip phase shifting phased array element constructed in accordance with the present invention;

FIG. 2 is a side view ofFIG. l;

FIG. 3 is a bottom view of FIG. l;

FIG. 4 is a chart illustrating nominal performance characteristics of the conventional bits incorporated in the circuitry of FIG. 1; and

FIG. 5 is an illustration, partially in schematic form, of another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referringv now to FIG. 1, there is illustratedy a phase shifting antenna element constructed in accordance with the present invention. The phase shifting antenna element may take innumerable forms, and may be utilized for either transmitting or receiving. For this example, there is illustrated a microstrip phased array element. The microstrip phased array element of the present exemplification is constructed utilizing microelectronic techniques. A substrate 1 is provided having an upper surface 2, a lower surface 3(FIG. 3) and an edge 4 (FIG. 2). The substrate 1 is constructed in dielectric material. In microelectronic embodiments, the substrate 1 is preferably ceramic. A conventional dipole antenna 10 is formed over opposite halves of the edge 4 and may also extend over the surface 2 and 3 and includes a first arm 1l anda second arm 12. Input energy is coupled to the arms l1 and l2 from a radio frequency feed 14 formed on the surface 1. The radio frequency feed 14 is coupled to first ends of the arms 11 and 12 on the upper surface 2. Second ends of the arms 11 and 12 on the lower surface 3 are connected to a ground conductor 16 formed on the surface 3 (FIG. 3). The circuit formed in area 32 is generally referred to as a balun 32. The balun 32 transforms the unbalanced feed provided by the radio frequency feed 14 and ground conductor 16 to a balanced feed required by the dipole antenna 10. The radio frequency feed 14, and antenna l0, and the ground conductor 16, are commonly formed of gold or copper.

The structure shown is analagous in function to the well-known configuration of a coaxial line excited dipole antenna. As discussed on pages l79 and 180 of Antenna Engineering, W.L. Weeks, McGraw-Hill, Inc. (New York, N Y.) 1968, proper balance in such a configuration is maintained by use of a split coax balun wherein the coaxial feeder is split and opposed sections of the shield are slotted as illustrated on page 180 in FIG. 4.29(c). The two dipoles are connected to the thus bifurcated sections of the shield and the exteriors of those sections act as a shorted, quarter-wavelength parallel-wire line and accomplish the required balancing function whereupon the tendency of currents to flow on the outside of the coaxial feeder is suppressed. The center conductor of the coaxial feeder is joined to one side of the bifurcated shield to complete the feed connection.

Comparing the structure of FIGS. 1-3 to that described in Weeks the feed strip 14 is equivalent to the center conductor of the coaxial feeder and the parallel conductive strips on the opposite side of substrate l (FIG. 3) are functionally equivalent to the slotted portion of the coaxial shield and are quarter-wavelength sections forming a balun.

In accordance with the present invention, the antenna element incorporates phase shifting means 20. As illustrated in FIG. 1, the phase shifting means 20 is a digital phase shifter including a 221/2 bit 22, a 45 bit 24, a 90 bit 26, and a 180 bit 28. A D.C. biasing supply 31 is coupled to each of the bits in the phase shifter 20. Each of the bits in the phase shifter 20 is illustrated in schematic form and is coupled to the biasing supply 31 by radio frequency choke means B1 in order to prevent the flow of radio frequency energy from the radio frequency feed 14 to the biasing supply 31. Also, in order to provide for independent biasing, the feed 14 is split and coupling capacitors C are inserted between the bits 22, 24, 26 and 28. Each of the bits 22, 24, and 26 comprises a well-known loaded line diode phase shifter. Additional RF choke means B2 are provided in the diode ground connections. The l80 bit 28 comprises means for reversing the polarity of the signal supplied to the diodes. FIG. 4, in which the abscissa is frequency and the ordinate is actual phase shift normalized with respect to nominal phase shift of each bit, illustrates nominal variations in phase shift versus band width of the applied frequency for the bits 22, 24 and 26. Such plots are only typical, and vary from bit to bit, depending on the delay line design and particular diodes included therein. The curved plots represent nominal characteristics for a conventional loaded line delay line, and the straight line plot represents a nominal characteristic for a conventional line length delay line. The operation of these bits is well-known in the art, and thus not discussed here. For example, see Burns et al, PIN Diodes Advance High-Power Shifting," Microwaves, Vol. 4, No. ll (Nov. 1965) pp. 40-41 For purposes of the present description, it is sufficient to state that each bit may be switched to provide or not provide the phase shift associated therewith.

The bit 28 of the phase shifter 20 comprises means for reversing the polarity of the signal applied to the phase shifter 20. In the present embodiment, the bit 28 is implemented in the following manner. A first switch comprising a unilateral conductive device 29 is connected for conduction in a first direction from the radio frequency feed 14 to the first arm 1l of the dipole l0. A second switch comprising a unilateral conductive device 30 is connected for conduction in the opposite direction from the radio frequency feed 14 to the second arm l2 of the dipole l0. Preferably, the unilateral conductive devices 29 and 30 comprise diodes 29 and 30 which may be formed on the substrate l by microelectronic techniques. The D.C. biasing supply 31 has selectable outputs to bias each of the bits 22, 24, 26 and 28 with selected polarity. When the biasing supply 31 provides a first polarity, the diode 29 is nonconductive and the diode 30 conducts. Similarly, when the bias provided by the biasing supply 31 is of a second polarity, the diode 29 conducts and the diode 30 is nonconductive.

OPERATION OF THE CIRCUIT A radio frequency input is supplied to the radio frequency feed 14 from a radio frequency source (not shown). A positive or negative potential is applied to each of the bits 22, 24, 26 and 28, depending on the phase shift desired. For example, if it is desired to provide a 270 phase shift, the first potential is applied to the bits 26 and 28, and a second potential is applied to bits 22 and 24. Any combination of the bits may be biased to produce desired phase shift. For purposes of this description, when a bit is biased such that it is producing a phase shift, it is referred to as enabled. When the bit is biased so as not to produce a phase shift, it is referred to as disabled. For purposes of this description, the convention shall be taken that the bit 28 is disabled when a positive potential is applied thereto and enabled when a negative potential is applied thereto from the biasing supply 31. When the bit 28 is disabled, the diode 29 conducts, shorting the radio frequency feed 14 to the arm 1l of the dipole l0. The diode 29 is effectively a portion of the arm l l. At the same time, the diode 30 is not conducting, consequently normal dipole currents are established in the manner of the coaxial line excited dipole discussed in the Weeks text mentioned previously. However, when the bit 28 is enabled, the states of the diodes 29 and 30 are reversed, and the diode 30 is effectively a portion of the arm 12. More specifically, the diode 29 is nonconductive, and the diode 30 conducts. Consequently, a 180 phase shift is produced by the bit 28 of the phase shifter 20 tantamount to the effect achieved by physically rotating the antenna through 180. The level of bias provided to the diodes 29 and 30 must be sufficient such that voltage swings of the signal will not change the state of the diode as determined by the biasing potential.

This operation is highly reliable in that the precise 180 phase shift is provided even if the diodes 29 and 30 are not ideal, whether in the conductive or nonconductive state. Only one mode of excitation of the dipole, i.e. currents monotonically decreasing from the center to the end of each arm l1 and 12 of the dipole 10, will radiate. Current flow due to either diode 29 or 30 not being an ideal open or short circuit will not contribute to the radiated energy. Furthermore, the antenna element is symetrical, and the mismatch will be constant for both states of the diodes 29 and 30. In

other words one of the diodes 29 and 30 is always conducting and the other is always nonconducting whether the bit 28 is enabled or disabled. Thus, the impedance seen by the radio frequency feed 14 remains constant. Consequently, a simple impedance matching means (not shown) may be used for supplying the antenna element to a source or utilization means (not shown). There is no need to match a first impedance when the bit 28 is enabled and a second impedance when the bit 28 is disabled.

A solid state switching means implementation of the bit 28 is preferred in low power applications such as phased array antennas. However, a mechanical implementation may be preferred for applications such as those in which a low switching rate of transmission of high levels of power may be required. Gas discharge devices such as transmit-receive tubes may be used for switching.

An embodiment in which switching of the diodes included in the bit 28 is accomplished by mechanical means is illustrated in FIG. 5, in which the same reference numerals are utilized to denote components corresponding to those of the embodiment of FIG. 1. The embodiment of FIG. 5, however, is constructed by conventional means rather than microelectronic techniques. In FIG. 5, the signal is coupled to the dipole by a balanced input line 40. For convenience of description, a first conductor of the balanced input line 40 is referred to as the radio frequency feed 14, and the second conductor of the balanced input line 40 is referred to as the ground conductor 16. The bits 22, 24 and 26 may be implemented in a conventional fashion comprising reactive devices enabled or disabled by conventional mechanical means or may comprise the same loaded line diode arrangement of FIG. 1. The bits 22, 24 and 26 could also be switched lengths of transmission line. The bit 28 of the phase shifter 20 of the present embodiment comprises a single pole double throw mechanical switch which provides means for reversing the polarity of the signal coupled to the dipole l0.

The present invention thus provides integration of radiating and phase shifting functions into a single structure. The invention also provides a zero error 180 phase shifting bit in a phase shifting circuit the response of which is not effected by changes in signal frequency. This operation is especially significant since it is the bit in which a given percentage error causes a larger absolute error than in other bits. Differing embodiments of the invention have been illustrated to suggest to those skilled in the art many forms which the present invention could take. The present invention may be employed as a transmitting or receiving antenna element and the term radiating is meant to apply to either. Further, since antennas are two terminal devices, the present invention may be utilized in systems incorporating other forms of antennas than a dipole. The portions of the antenna connected to each terminal comprise antenna arms within the meaning of the above description.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a phased array element including an antenna having first and second arms, a phase shifter connected in series with a radio frequency feed to the antenna including at least one bit for providing a phase shift of less than 180 coupled in series with a 180 zero-error phase shifting bit comprising first and second diodes connected between said phase shifting Abit providing less than 180 phase shift and first and second arms of the antenna respectively, and means for selectively biasing one of said diodes in a forward direction and the other of said diodes in a reverse direction.

2. A high frequency RF radiating structure comprising:

a thin insulative substrate having a dipole radiating element supported on an edge thereof:

an unbalanced RF feed for supplying a high frequency RF signal to said dipole including a first conductor having electrically operated phase shifting means supported on one side of said substrate and a second conductor supported on the opposite side of said substrate, said second conductor including a quarter-wavelength balun supported in alignment with said first conductor; and

means for connecting said RF feed to said dipole radiating element including selectively operable current switching means for alternately connecting said first conductor to one or the other of the two halves of said dipole, each reversal of said switching means causing a 180 phase shift in the signal radiated by said dipole. 

1. In a phased array element including an antenna having first and second arms, a phase shifter connected in series with a radio frequency feed to the antenna including at least one bit for providing a phase shift of less than 180* coupled in series with a 180* zero-error phase shifting bit comprising first and second diodes connected between said phase shifting bit providing less than 180* phase shift and first and second arms of the antenna respectively, and means for selectively biasing one of said diodes in a forward direction and the other of said diodes in a reverse direction.
 2. A high frequency RF radiating structure comprising: a thin insulative substrate having a dipole radiating element supported on an edge thereof: an unbalanced RF feed for supplying a high frequency RF signal to said dipole including a first conductor having electrically operated phase shifting means supported on one side of said substrate and a second conductor supported on the opposite side of said substrate, said second conductor including a quarter-wavelength balun supported in alignment with said first conductor; and means for connecting said RF feed to said dipole radiating element including selectively operable current switching means for alternately connecting said first conductor to one or the other of the two halves of said dipole, each reversal of said switching means causing a 180* phase shift in the signal radiated by said dipole. 